Crane counterweight and suspension

ABSTRACT

Disclosed is a mobile articulated crane having a boom for carrying a load when the crane is stationary and while the crane is mobile. The boom has an end for engaging with a load and an opposed end. The crane further comprises a counterweight attached to the boom at or close to the opposed end of the boom. A rear body of the crane can comprise first and second rear axles, each for supporting the rear body on the ground. The first rear axle can be arranged to be displaced relative to the second rear axle such that wheels of the first rear axle selectively engage or disengage with the ground.

RELATED APPLICATION DATA

This application is a division of U.S. patent application Ser. No.16/333,720, filed Mar. 15, 2019, the entirety of which is incorporatedherein by reference to the extent permitted by law. U.S. patentapplication Ser. No. 16/333,720 is the Section 371 National Stage ofPCT/AU2017/050999 filed Sep. 14, 2017. This application claims thebenefit of priority to Australian Patent Application No. 2016903705filed Sep. 15, 2016, the entirety of which is incorporated by referenceherein to the extent permitted by law.

TECHNICAL FIELD

This disclosure generally relates to pick and carry cranes and, moreparticularly, to improved counterweight and suspension systems for pickand carry cranes.

BACKGROUND ART

A pick and carry crane is a type of crane that is able to move (i.e.travel) while it has a load suspended from a boom of the crane. Somepick and carry cranes are able to drive on public roads at highwayspeeds, with these cranes being classified as special purpose vehicles.The design of pick and carry cranes can vary depending on theapplication of the crane. Some designs of pick and carry cranes are moremaneuverable compared to other crane types. For example, when the pickand carry crane is articulated, the whole crane can fit within a turningcircle of the crane. This design feature can enable articulated pick andcarry cranes to be used in tight or confined spaces to lift and moveloads, such as on the floor of a manufacturing facility.

Pick and carry cranes can also take the form of “taxi cranes”, which isa reference to the crane travelling with all equipment required tooperate through the full range of capability of the crane. In some taxicranes, the same operator station is used to control the crane whentravelling (such as on a public road) as when operating the crane at afacility. This “single cabin” arrangement helps to simplify craneconfiguration, and also provides flexibility for the operator (i.e. bynot having to move back and forth between a driver's cab and a cranecab). Many cranes cannot operate as a taxi crane since they cannottransport all components required to operate, hence support vehicles aregenerally required to carry extra components, such as counterweights andrigging including slings & hooks.

As the maximum rated capacity (MRC) of the crane increases, its weightgenerally increases. Pick and carry cranes tend to carry lighter loadsin comparison to other cranes (i.e. less than 25 tonnes). However, theincreased maneuverability of pick and carry cranes has led to a demandfor pick and carry cranes that are able to carry more than or that havean MRC greater than 25 tonnes, whilst also being able to lift and carrysuch larger loads in confined or tight spaces.

However, as the rated capacity of a pick and carry crane increases, itssusceptibility to sideways tipping generally also increases. Theincrease in susceptibility to sideways tipping comes about since thereare physical limitations to the overall width of a pick and carry cranewhen e.g. driving on public roads such as highways or when driving in afacility. Crane tipping and thus crane toppling presents occupational aswell as public health and safety issues.

With mobile cranes, for example, outriggers can be used to minimisesusceptibility to sideways tipping. However, such outriggers are usedwhen the crane is operating at a stationary position. Because pick andcarry cranes need to travel with a load, this means that outriggerstypically cannot be used.

It is to be understood that references herein to the prior art do notconstitute an admission that such art forms a part of the common generalknowledge of a person of ordinary skill in the art, in Australia or anyother country.

SUMMARY OF THE DISCLOSURE

Disclosed herein is an improved pick and carry crane. The pick and carrycrane comprises a front body that defines a front part of the crane. Thefront body is pivotally connected via a pivot arrangement to a rear bodyof the crane. This arrangement defines the crane as an articulated pickand carry crane.

The pick and carry crane defines a side tipping line when the front bodyhas been pivoted (i.e. articulated) relative to the rear body about thepivot arrangement. The side tipping line is defined as an imaginarylongitudinal axis that extends between a point at which the front bodycontacts the ground to a point at which the rear body contacts theground, being the points about which the crane may topple (e.g. whenunder load and in use). A maximum amount of the load can be transferredthrough these front and rear points at the point of tipping. Typicallythe point at which the front body contacts the ground is via innertyre(s) of the front body (i.e. when articulated). Typically the pointat which the rear body contacts the ground is via inner tyre(s) of therear body (i.e. again, when articulated).

In accordance with the disclosure, a first counterweight is mounted withrespect to the crane and is arranged to move with respect to the sidetipping line so as to maintain a counteracting side tipping moment abovea threshold value when the crane is lifting and/or carrying a load. Thisthreshold value corresponds to a side tipping moment that would causethe crane to topple sideways about the tipping line.

Such a pick and carry crane may carry greater loads whilst, at the sametime, having a reduced susceptibility to sideways tipping, such as whencompared to currently known pick and carry cranes.

It has been observed that the position of the centre of mass/gravity inrelation to the tipping line can represent a critical relationship inrelation to crane stability. For example, it is known that the length ofpick and carry cranes has generally increased (i.e. to provide a greaterdistance from the centre of mass/gravity to a so-called forward tippingline—end-to-end tipping). This increased length enables the crane toaccommodate (i.e. lift and carry) larger loads.

However, because of the physical constraints on width imposed by publicroad use, the increase in pick and carry crane length has occurredwithout a commensurate increase in crane width (distance from cranecentre of gravity to the side tipping line). For example, in the past,the original lower capacity pick and carry cranes tended to be widerthan they really needed to be, whereas later-developed higher capacitycranes approached a design criterion where they were narrower than wasoptimal.

It has also been observed that, as the difference between forwardtipping stability and side tipping stability increases, the ratedcapacity of a pick and carry crane can change rapidly with small changesin angle of the boom. For example, the driving of the crane onto slopingor uneven ground can create a sudden reduction in capacity, with smallchanges in the roll angle of the crane likely to increase likelihood oftipping. In addition, the crane can become too sensitive to small loadswings.

Since pick and carry cranes are designed to be driven on public roads,which allows them to quickly and easily drive between sites ofoperation, as well as to quickly set up to lift and carry loads, theiroverall width is limited. In this regard, to be able to drive on publicroads, the crane must have a size that meets various road and safetyregulations. For example, such regulations specify that the width of acrane generally needs to be less than 3000 mm. In an embodiment, thewidth of crane is greater than 2500 mm, and may be 2600 mm, 2700 mm,2750 mm. More specifically, the width of crane may be about 2740 mm.

Given the width of the crane cannot be increased indefinitely, anycounteracting side tipping moment cannot also be increased simply bycontinuing to increase the width of the crane. Therefore, the presentinventors have conceived of the idea of a first counterweight that ismoveable relative to the side tipping line to increase the counteractingside tipping moment of a pick and carry crane. The first counterweightmay improve the counteracting side tipping moment by at least 25%compared to pick and carry cranes that do not have the firstcounterweight.

In an embodiment, the crane may further comprise a boom support arm forsupporting a boom of the crane. The boom support arm can be arranged atone end of the front body.

In an embodiment, the first counterweight may be mounted to an oppositeend of the boom support arm, so as to be located rearwardly of the pivotarrangement. Thus, when the crane articulates, the first counterweightmay move, relative to the side tipping line, with the boom support arm.

In an alternative embodiment, the crane may further comprise a moveableframe that is mounted to the crane for movement with respect to the sidetipping line. The first counterweight may be mounted to the moveableframe such that it can be moved laterally therefrom so as to maintainthe counteracting side tipping moment above the threshold value.

The rear body may also be configured to act as a counterweight. In anembodiment, the crane may further comprise a second counterweight thatcan be mounted with respect to the rear body of the crane. The secondcounterweight may be mounted to one of:

-   -   a. a rearward end of the rear body of the crane;    -   b. a moveable frame that is mounted with respect to the rear        body of the crane, the mounting to the moveable frame being such        that the second counterweight can be located at the rearward end        of the rear body of the crane or be moved laterally therefrom.

The second counterweight can provide counteracting end-to-end tippingmoment of a pick and carry crane. The second counterweight can also actcooperatively with the first counterweight.

As set forth above, mobile cranes are generally rated according to theirMaximum Rated Capacity (MRC). For example, in Australia it is arequirement that the MRC be displayed on the crane. The MRC is thehighest rated capacity (RC) value that a crane can lift. In most casesthere will be a very limited range of configurations in which the MRCwill be achieved, and a lesser RC will exist for all otherconfigurations. Hence a crane referred to as a “20 tonne” crane has aMRC of 20 tonne.

However the RC of a crane is based on a combination of the stabilityload moment capacity of the crane as well as the strength limit of allcomponents of the crane. For example, two pick and carry cranes may havea 25 MRC, where a first crane can lift 25 tonne at a 1.0 metre radius,and the second crane can lift 25 tonne at a 1.4 metre radius. The twocranes have the same MRC but the second crane has a higher load momentcapacity. Hence, at any other radius, such as say 3.0 metre, the secondcrane has a much higher RC because of its higher load moment capacity.

Therefore, in practice it is load moment capacity that denotes theusefulness of a crane. The stability load moment capacity of a crane isderived from two variables; the total mass (referred to generally as theweight) of the crane and the distance from the centre of gravity (CG) ofthe crane mass to the tipping line, where:Load Moment=(crane mass)×(radius of CG to tipping line).

For example, if a crane has load moment capacity of 30 tonne metre, thenat a radius of 3 metres, it will safely lift 10 tonne, and at radius of5 m it will safely lift 6 tonne.

A pick and carry crane using the first counterweight as disclosed hereinmay have a MRC and load moment capacity that can exceed existing pickand carry cranes (i.e. that do not employ such a first counterweight).In an embodiment, the MRC of the pick and carry crane as disclosedherein may be 40 tonne (t). In an embodiment, the load moment of thepick and carry crane as disclosed herein may be 66 tonne meters (t.m).However, these values are indicative, and should not be interpreted asrepresenting upper limits.

Also disclosed herein is a further improved pick and carry crane. Thepick and carry crane comprises a front body that defines a front part ofthe crane. The front body is pivotally connected via a pivot arrangementto a rear body of the crane. This arrangement again defines the crane asan articulated pick and carry crane.

The front body comprises a front axle for supporting the front body onthe ground. The rear body comprises first and second rear axles, eachfor supporting the rear body on the ground.

In accordance with the disclosure, the first rear axle is arranged to bedisplaced relative to the second rear axle such that wheels of eitherthe first rear axle or the second rear axle can selectively engage ordisengage with the ground.

To increase the counteracting forward tipping moment, the weight of therear body can be increased. However, simply increasing the weight of therear body can cause the axle loads to be greater than that required byroad regulations. Therefore, the present inventors have conceived of theidea of providing additional rear axles, such as by providing first andsecond rear axles. The first and second rear axles can accommodate anincreased crane mass to allow the crane to be driven on public roads athighway speeds.

However, simply providing a second rear axle can hamper the crane whenlifting and carrying loads, that is, when operating in a crane mode. Forexample, having a second rear axle can increase the wheelbase length ofthe crane, and this can decrease the maneuverability of the crane.Accordingly, the present inventors have conceived of the idea of havingone of the rear axles, such as the first rear axle, arranged to bedisplaced relative to the second rear axle, such that wheels of thefirst rear axle are able to selectively engage or disengage with theground or vice versa.

This arrangement can maintain the maneuverability of the crane (i.e.when in crane mode) in a manner similar to known two axle pick and carrycranes, but can allow the crane to have an increased weight to provide agreater counteracting forward tipping moment, which increased weightcrane can also be driven on public roads.

In an embodiment of the crane, whilst the first rear axle to bedisplaced can be that axle which is further from a rear of the rear body(i.e. further than the second rear axle), typically the first rear axleis that axle which is arranged closer to the rear of the rear body (i.e.closer than the second rear axle). This location of the first rear axlecan further help to maintain the maneuverability of the crane (e.g. whenin crane mode) in a manner similar to known two axle pick and carrycranes.

In a further embodiment of the crane, each of the first and second rearaxles may be able to be displaced. Thus, when operating in a crane mode,an optimum axle to be displaced can be selected by the operator or maybe automatically selected by a programmable controller.

In an embodiment, the crane may be adapted to operate in a travel modein which the wheels of the first rear axle selectively engage theground, and a crane mode in which the wheels of the first rear axleselectively disengage the ground. When in travel mode, the crane mayhave a ground speed of 60, 70, 80, 90, 100 or 110 km/h.

In an embodiment, the crane may be adapted to change from the crane modeto the travel mode at a predetermined ground speed of the crane. Thechange from the crane mode to the travel mode may occur automatically(i.e. the disengaged axle may be automatically lowered). Thepredetermined ground speed of the crane at which the change occurs maybe less than around 10 km/h and may occur at around 5 km/h.

In an embodiment, each of the first and second rear axles may comprise arespective suspension system. The suspension system for the first rearaxle may be arranged to displace the first rear axle to cause its wheelsto selectively engage or disengage with the ground. In an embodiment,the crane may further comprise a respective suspension system for thefront axle. The front axle suspension system may be arranged to allowfor a frame of the front body to rest on and transfer load directly tothe front axle during the crane mode. This action can accommodate aheavier overall weight of the loaded crane.

A crane that has the first rear axle arranged to be displaced relativeto the second rear axle may be configured otherwise as set forth above(i.e. with an added first counterweight). As set forth above, the frontbody may be pivotally connected to the rear body to define the crane asan articulated pick and carry crane. Wheels for the crane may eachcomprise rubber tyres.

The pick and carry crane as disclosed herein may be configured to have aMRC of at least 30, 35, 40, 45 or 50 tonne.

The pick and carry crane may comprise steering for at least one set ofrear wheels.

The steering may be for a rearmost set of wheels. The steering for therearmost set of wheels may be in addition to steering provided for afront set of wheels. The steering for the rearmost set of wheels may becontrolled in dependence on a degree of articulation of the crane. Thesteering for the rearmost set of wheels may have a predetermined maximumdeflection for the rearmost set of wheels.

Also disclosed herein is a method of operating a pick and carry cranehaving a front body that defines a front part of the crane. As above,the front body is pivotally connected via a pivot arrangement to a rearbody of the crane (i.e. articulated).

In use of the crane, the front and rear bodies define a side tippingline when the front body has been pivoted relative to the rear bodyabout the pivot arrangement. The side tipping line is again defined asan imaginary longitudinal axis that extends between a point at which thefront body contacts the ground to a point at which the rear bodycontacts the ground, being the points about which the crane may topple.A first counterweight is mounted with respect to the crane. As set forthabove, typically the point at which the front body contacts the groundis via inner tyre(s) of the front body, and typically the point at whichthe rear body contacts the ground is via inner tyre(s) of the rear body(i.e. when the crane is articulated).

In accordance with the disclosure, the method comprises operating thecrane so as to lift and/or carry a load with respect to the front bodyof the crane. The method also comprises pivoting the front body relativeto the rear body to define the side tipping line. The method furthercomprises moving the first counterweight with respect to the sidetipping line so as to maintain a counteracting side tipping moment abovea threshold value when the crane is lifting and/or carrying the load.The threshold value corresponds to a side tipping moment that causes thecrane to topple sideways about the side tipping line.

In an embodiment of the method, the first counterweight may be movedwith respect to the side tipping line by rotation from a positionrearward of the pivot arrangement. This rotation can, for example, occurautomatically with crane articulation.

Also disclosed herein is a method of operating a pick and carry cranehaving a front body that defines a front part of the crane. As above,the front body is pivotally connected via a pivot arrangement to a rearbody of the crane (i.e. articulated). The rear body comprises first andsecond rear axles, each for supporting the rear body on the ground

In accordance with the disclosure, the method comprises displacing thefirst rear axle relative to the second rear axle to engage or disengagewheels of the first rear axle with the ground (or vice versa).

In accordance with the method, the wheels of the first rear axle may beengaged with the ground when the crane is operated in a travel mode, andthe wheels of the first rear axle may be disengaged with the ground whenthe crane is operated in a crane mode. As set forth above, thisengagement and disengagement may occur automatically as part of acontrolled operation procedure of the crane.

Also disclosed herein is a pick and carry crane that is operatedaccording to the methods as set forth above.

A further embodiment extends to a mobile articulated crane having a boomfor carrying a load when the crane is stationary and while the crane ismobile, said boom having a first end for engaging with a load and anopposed end, the crane further comprising a counterweight attached tothe boom at or close to the opposed end of the boom.

The counterweight may be displaceable and an extent of displacement ofthe counterweight may be dependent upon one or more of: an extent ofarticulation of the crane; on an extension of the boom and a speed ofthe crane.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments will now be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of an embodiment of a pick and carrycrane.

FIG. 2 shows a side view of the pick and carry crane.

FIG. 3 shows a plan view of the pick and carry crane.

FIG. 4 shows a plan view of the pick and carry crane when pivoted(articulated).

FIG. 5 shows a plan view of another pick and carry crane when pivoted(articulated).

FIG. 6 shows a side view of the pick and carry crane of FIG. 1 carryinga load.

FIG. 7a shows a side view of the pick and carry crane carrying a load.

FIG. 7b shows a side view of the pick and carry crane tipping forwardwhen carrying a load.

FIG. 8 shows a plan view of yet another pick and carry crane whenpivoted (articulated).

FIG. 9 shows a further embodiment of a pick and carry crane.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1, 2 and 3 show a pick and carry crane 10. The crane 10 has afront body 12 which is the front part of the crane 10. The front body 12is pivotally connected via a pivot arrangement 30 (exemplified by thedashed line in FIGS. 2 and 3) to a rear body 14 of the crane 10. Thepivot point 30 may be provided with moveable linkages, such as hydraulicrams, to control the pivot angle of the front body 12 to the rear body14. Adjusting the pivot angle using the moveable linkages helps to turnthe crane 10. A side tipping line 34 (see FIG. 4) is defined when thefront body 12 is pivoted relative to the rear body 14.

In the embodiment of the pick and carry crane 10 as depicted in theFigures, the side tipping line 34 is an imaginary longitudinal axis thatextends between a point at which the inner tyres T1 of the front bodycontact the ground, via wheel 20, and a point at which one of the innertyres T2 and T3 of the rear body contacts the ground, via either wheel16 and/or 18 (i.e. depending on which tyre is engaged with the groundwhen the crane is in crane mode—described below). Thus, the tyres T1-T3of the wheels 20, 16 and 18 define the points about which the crane maytopple sideways.

The crane 10 is provided with a first counterweight 22 mounted withrespect to the crane 10. The counterweight 22 is arranged to move withrespect to the side tipping line 34 so as to maintain a counteractingside tipping moment above a threshold value when the crane is liftingand/or carrying a load. The threshold value corresponds to a sidetipping moment that causes the crane to topple sideways about the sidetipping line 34.

Attached to the rear end of the front body 12 is a boom support arm 24.The boom support 24 may be a separate structure that is mounted e.g.welded or bolted to the front body 12. In an embodiment, the boomsupport arm 24 forms part of the chassis of the front body 12. The boomsupport arm 24 pivotally supports boom 26, where the boom 26 is raisedand lowered about the pivot point, represented by pin 27 (FIG. 2), usinglinear actuators in the form of hydraulic rams 28. The boom 26 may havea fixed length or may be telescopic. Other forms of linear actuators canbe used in place of or in addition to rams 28. In FIGS. 1 to 3, thecounterweight 22 is mounted to an opposite end of the boom support arm24 so that counterweight 22 is located rearwardly of the pivotarrangement 30.

The arrangement of the counterweight 22 and how it moves with respect tothe side tipping line 34 is shown in FIG. 4. The side tipping line 34extends between the tyre T1 of inside front wheel 20 and one of thetyres T2 or T3 of a respective inside rear wheel 16 and/or 18 (i.e.depending on which tyre is engaged during the crane mode—describedbelow).

When the crane 10 is driving approximately straight ahead, thecounterweight 22 is positioned approximately over the centre line,represented by dashed line 31, of the rear body 14. However, when thecrane 10 is articulated (i.e. pivots) about the pivot point 30 whenturning, as shown in FIG. 4, the counterweight 22 rotates away fromcentre line 31, about pivot point 30, so as to be displaced from thetipping line 34 by distance d₁. Distance d₁ is calculated as aperpendicular line from the tipping line 34 to the centre of gravity ofthe counterweight 22, as represented by dot 37. It should be noted thatthe centre of gravity of counterweight 22 will differ depending on theshape and orientation of the counterweight used in crane 10, such thatthe CoG 37 depicted in FIG. 4 is exemplary only.

The distance d₁ is also dependent on the distance d_(r) of the centre ofgravity 37 of counterweight 22 to the pivot point 30. Thus, d₁ generallyincreases as d_(r) increases for a given angle θ. The turning angle θformed between the front body 12 and rear body 14 also determines d₁,where d₁ generally increases as θ increases. The maximum turning angle θcan be dependent on the size of crane 10 and the intended use of thecrane. The maximum turning angle θ may be 90, 80, 70, 60, 50, 40 or 30degrees or less. In the crane embodiment depicted, the maximum turningangle θ is approximately 40 degrees. When fully articulated, the wholecrane 10 fits within the envelope of the turning circle. This feature ofthe crane 10 can be particularly useful in congested spaces. In practicethis means that, when the steering angle is kept constant, and if thefront corner of the crane can pass an object, then the whole of thecrane will clear. This can leave the operator free to concentrate onwhat is in front of them, and also to concentrate on what is happeningwith the load.

In an alternative embodiment, the first counterweight 22 can be providedon a moveable framework that is mounted to the front body 12. Themoveable framework can be controlled to pivot laterally, fromside-to-side, on the front body 12.

When crane 10 is turning when carrying a load 32, as in FIG. 4, the load32 exerts a side tipping moment TM₁ on the crane 10. The side tippingmoment TM₁ is determined by the mass of load 32 and the perpendicularline distance d₂ that the centre of gravity of the load (as representedby dot 39) is away from the tipping line 34. In this regard, TM₁=mass ofload 34×distance d₂ from tipping line. The side tipping moment TM₁represents the threshold value. Further, TM₁ increases as θ increasessince d₂ increases as θ increases. Therefore, as counterweight 22 pivotsaway from tipping line 34 by distance d₁ when the front body 12 pivotsabout pivot point 30, a counteracting side tipping moment, representedby CM₁, is provided. Accordingly, provided that CM₁≥TM₁, the crane 10should not tip about tipping line 34 and thus topple over.

Since TM₁ is determined by a variety of factors including load mass,boom length and angle θ, sensors such as load, angle and/or mechatronicsensors may be positioned on crane 10 to provide inputs to calculateTM₁. TM₁ can be calculated in real time. TM₁ can be calculated using oneor more on-board computers and/or computer systems. The one or morecomputers and or computer systems can provide operator feedback toensure CM₁≥TM₁ in use of crane 10. Counteracting moment CM₁ is generallyonly determined by angle θ because the mass of the counterweight andposition of counterweight 22 relative to pivot point 30 is generallyfixed.

The crane 10 may use programmable computer logic (PCL) to ensure CM₁≥TM₁in use of the crane 10. The PCL may be provided as software or firmwareon the one or more computers and/or computer systems. The PCL may useinput signals from sensors positioned on crane 10. If the PCL determinesthat TM₁ is approaching and/or exceeding CM₁, e.g. by an operatorturning the crane 10 to increase θ, the PCL may instruct the operator toreduce θ. Alternatively, the PCL may reduce θ by, for example,controlling the movably linkages provided at the pivot point. In theembodiment of the pick and carry crane 10 as depicted in the Figures,the MRC of crane 10 is 40 tonnes, and the load moment of crane 10 is 66tonne meters. These values can vary when the overall configuration ofthe pick and carry crane 10 is varied, and so should be seen asnon-limiting.

Because the width of crane 10 is generally restricted by regulationsthat permit the crane 10 to drive on public roads at highway speeds, thewidth of the crane 10 cannot be increased to provide an increasedcounteracting side tipping moment. A wider crane will typically providea greater counteracting side tipping force compared to a narrower craneof the same weight. Therefore, use of counterweight 22 can help toincrease the counteracting side tipping moment for pick and carry craneswhilst still allowing the crane to comply with road regulations.

The rear body 14 can be provided with a second counterweight 33 that hasa centre of gravity represented by dot 35. Counterweight 33 ispositioned at the rear end of rear body 14. The purpose of the secondcounterweight 33 is to provide a counteracting front tipping moment toprevent the crane 10 from tipping forward over the front tipping point(see FIG. 7b ), which is the point of ground contact at the front body12. In the embodiment in FIG. 7a , this front tipping point takes theform of an imaginary forward tipping line 40 that extends between theground contact points of tyres T1 of the front wheels 20 at either sideof the crane.

In an alternative embodiment, the second counterweight 33 can beprovided by an increased weight of the rear body 14 (e.g. integratedinto the rear body 14).

As shown in FIGS. 4 & 5, the rear counterweight 33 has a centre ofgravity 35 located close to the side tipping line 34. The counteractingside tipping moments CM₂ and CM₃ shown respectively in FIGS. 4 & 5 areeach determined by the perpendicular line distance d₃ from the tippingline 34 to the centre of gravity 35. If counterweight 22 was omittedfrom the crane 10, as shown in FIG. 5, the only counteracting sidetipping moment would be that provided by CM₃. Conversely, in FIG. 4, thecounteracting side tipping moment=CM₁+CM₂.

It should be noted that counterweight 33 is mounted on the rear bodybehind the rear contact point of the tyres T2, T3 of rear wheels 16 and18. Thus, CM₃ decreases as θ increases. If the second counterweight 33was located in front of this rear contact point, i.e. closer to pivotpoint 30, this would decrease the counteracting forward tipping moment,which would likely decrease the overall MCR and moment load of crane 10.Hence, it is generally preferable to place second counterweight 33further away from pivot point 30 rather than closer to it. In short,without counterweight 22, crane 10 can be more prone to toppling overthe tipping line 34 as the angle θ increases, because the onlycounteracting side tipping moment would then be CM₃. By providingcounterweight 22, the pick and carry crane 10 is able to lift, carry andturn with loads far in excess of conventional pick and carry cranes. Itcan be seen that the counterweights 22 and 33 are positioned to workcooperatively in use of the crane.

In a further alternative embodiment, the second counterweight can bemounted to a second moveable framework. The second moveable frameworkcan be mounted with respect to the rear body 14 of the crane 10. Thesecond counterweight is mounted to the moveable frame in such a way thatthe second counterweight can be located at the rearward end of the rearbody of the crane or be moved laterally therefrom. In this way, thesecond counterweight may be able to move to provide both a counteractingforward tipping moment CM₄ (FIG. 7a ) and a counteracting side tippingmoment CM₂ (FIG. 4). The moveable frame may comprise linear actuatorssuch as hydraulic rams that can use the second counterweight. The secondcounterweight may be positioned at an end of an arm that can be rotatedabout a pivot point located on the rear body 14.

As set forth above, in FIG. 4, the total counteracting side tippingmoment is a sum of the first and second counteracting side tippingmoments i.e. CM₁+CM₂. However, because distance d₁ is generally muchgreater than d₂, the mass of counterweight 22 can be significantly lessthan the combined mass of the second counterweight 33 plus the rear body14 to provide an adequate overall counteracting side tipping moment.Expressed another way, the radius to the side tipping counterweight 22is much larger, hence the mass can be smaller and it will still have asignificant benefit.

The first counterweight 22 can have a mass greater than 100, 250, 500,750 or 1000 kg. In the crane embodiment of FIG. 4, the firstcounterweight 22 has a mass of about 3300 kg. In the crane embodiment ofFIG. 4, the mass of the second counterweight 33 is about 3000 kg. Theweight of the rear body 14 is 14000 kg. Further, the centre of gravityof the rear body can be shifted rearwardly by the second counterweight33.

As mentioned above, not all pick and carry cranes need be provided witha second counterweight as depicted in FIG. 4. For example, in the craneembodiment of FIG. 8, the counteracting front tipping moment is providedonly by the mass of the rear body 14. The centre of gravity 50 of therear body in the embodiment in FIG. 8 is positioned approximately overthe centre of the rear wheels. However, even when the crane isarticulated by angle θ, the distance d₆ is approximately similar to d₃.Therefore the counteracting side tipping moment CM₆ provided by the rearbody 14 in FIG. 8 is approximately similar to CM₂ as shown in theembodiment of FIG. 4. Accordingly, in order to provide an increase inthe counteracting side tipping moment in the absence of counterweight22, the mass of the rear body 14 is significantly increased. However, asdescribed below, the weight of the rear body can be limited due to roadregulations. Hence, the use of counterweight 22 to provide acounteracting side tipping moment can allow the crane 10 to lift andcarry greater loads compared to cranes without counterweight 22 withoutthe need to significantly increase the weight of the rear body.

The centre of gravity of the rear body described herein is exemplaryonly. Accordingly, the actual position of the centre of gravity will bedetermined by the shape and orientation of the rear body and thecomponents and mass comprising the rear body.

While the embodiments shown in FIGS. 1 to 4, 6 & 7 have the firstcounterweight 22 fixed to the boom support arm, as set forth above thefirst counterweight may be moved with respect to the tipping line 34using other means. For example, the crane may further comprise amoveable frame that is mounted to the crane for movement with respect tothe side tipping line 34. The moveable frame can be mounted to the frontor rear body. There may be separate moveable frames on both the frontand rear bodies. The first counterweight can be attached to the moveableframe so as to provide a counteracting side tipping moment e.g. CM₁. Themoveable frame may comprise linear actuators such as hydraulic rams. Inthis way, the first counterweight may be attached to the linearactuators and may be moved laterally away from the tipping line when thefront body 12 pivots about pivot point 30 to form angle θ. The moveableframe may be mounted to have a rotational or pivotal movement. Whenrotational/pivotal movement is used, the first counterweight may beattached at an end of an arm mounted to either the front body 12 or rearbody 14. When the front body 12 pivots about pivot point 30, the arm canmove laterally away from the side tipping line 34. A moveable frame thatuses rotational/pivotal movement can operate in a similar manner to thecrane embodiment shown in FIGS. 1 to 4. However, by having the firstcounterweight separate from the boom support arm 24, the crane may bemore compact whilst still maintaining the same load moment capacity.

In a further alternative embodiment, two first counterweights can beprovided, with one counterweight being attached to boom support arm 24as in FIGS. 1 to 4, and the other being mounted to the moveable frame.The moveable frame may have mechatronic sensors that can communicatewith one or more on-board computers and/or computer systems. The one ormore computers and/or computer systems may control the moveable frame soas to optimise the counteracting side tipping moment. When a moveableframe is used, the first counterweight may be considered a dynamiccounterweight. If a dynamic system is used, then it may be necessary tocontrol the movement of the counterweights such that, in oneconfiguration at least, the entire crane fits within the turning circleat full articulation angle.

The crane embodiment described in FIGS. 1-4, 6 & 7 is shown with tworear axles. Generally, by providing a crane 10 that has more than tworear axles allows the crane to lift and carry larger loads compared to aconventional two axle pick and carry crane. In the crane 10 of FIGS. 1to 4, 6 & 7, the front body 12 has a front axle for supporting the frontbody on the ground via front tyres T1 of wheels 20. The rear body 14 hasfirst and second rear axles, each for supporting the rear body on theground, via first rear tyre T2 of wheel 16 and second rear tyre T3 ofwheel 18, respectively. The first rear axle is arranged to be displacedrelative to the second rear axle such that the tyre T2 of wheel 16 canbe selectively engaged (FIG. 2) or disengaged (FIG. 6) with the ground21.

In a variation, the second rear axle can be arranged to be displacedrelative to the first rear axle such that the tyre T3 of wheel 18 can beselectively engaged or disengaged with the ground 21.

The turning circle of crane 10 is determined by the distances betweenthe pivot point 30 and the respective wheels. The tyres of wheels 18 and20 are always in contact with the ground 21. Therefore, when the tyre ofwheel 16 is disengaged with the ground 21 (e.g. FIG. 6), the turningcircle of crane 10 is determined by distance D_(a) and the degree ofarticulation e.g. maximum angle θ. In an embodiment distance D_(a) is4750 mm. The overall length of crane 10 from the rear end of the rearbody 14 to the tip of the boom 26 in a retracted state, e.g. FIG. 2, canbe 11700 mm. The length from the rear end of the rear body 14 to thefront end of the front body 12 can be 8430 mm. The crane 10 can have aheight from the road 21 to the top of boom 26 of 3470 mm. While the term“road” has been used, the term road can include any surface on whichcrane 10 is driven in either crane or travel modes. For example, “road”may include asphalt, gravel, concrete and compacted dirt, and may be“off-road”.

As shown in FIG. 6, the distance from the pivot point 30 to the frontwheel 20 and the distance from the pivot point to wheel 18 is the same.This can help to ensure that the rear body 14 follows the front body 12when the front body moves through a tight space when cornering e.g.through a gap just wide enough for the crane 10. However, in someembodiments, the distance from the pivot point 30 to the front wheel 20and the distance from the pivot point to wheel 18 is not the same. Whenthe tyre of wheel 16 is engaged with the ground 21 (as shown in FIG. 2),the wheelbase length increases to distance D_(b). Distance D_(b) iscalculated as the average distance both wheels 16 and 18 are spaced frompivot point i.e. the average of distance D_(c) and D_(e). In anembodiment, distance D_(b) is 5450 mm, D_(c) is 2475 mm, D_(d) is 2475mm, and D_(e) is 3875 mm.

By having the wheels closest to the rear of the rear body 14, i.e. wheel16, move between an engaged and disengaged state with road 21, the rearwheels that are closest to the pivot point 30, i.e. the tyres of wheels18, are always in contact with the ground. Because the tyres of wheels18 are always in contact with the ground, the wheelbase length of thecrane 10 decreases when the tyres of wheels 16 are lifted off theground. This can help to decrease the radius of turning and improve theturning circle. In some embodiments, the turning circle of crane 10 issimilar to a standard pick and carry crane that only has two axles and alower load moment capacity.

Having more than two axles can help to spread the forces exerted ontothe crane more evenly onto road 21. By providing more than two axles,the crane 10 is able to comply with road regulations. For example, inAustralia, the maximum load that each axle can carry for special purposevehicles is limited to 12 tonnes. Therefore, the weight of the crane islimited to 24 tonne for a two axle crane. By having three axles, theweight of the crane can be up to 36 tonne whilst still complying withroad regulations. This can allow crane 10 to drive on sealed roads so asto travel between sites of operation e.g. a manufacturing floor orbuilding site.

However, at sites of operation, regulated axle load limits do not alwaysneed to be met, since the surface on which the crane 10 operates may berated for more than 12 tonne of load per axle. For example thickconcrete slabs can handle axle loads far greater than 12 tonne per axle.Since only two axles may be needed in operation, i.e. when the crane 10is operating in crane mode, the tyres of rear wheel 16 can be lifted offthe road 21 to improve the turning circle of crane 10. In this way, thecrane 10 is configured to operate in a travel mode when the tyres ofwheel 16 are selectively engaged with the road/ground, and a crane modewhen the tyres of wheel 16 are selectively disengaged the road/ground.

Because the tyres transfer the weight of the crane 10 and load 32 ontothe ground, they may be rated up to 14000 kg. The weight limit of a tyrefor a pick and carry crane can also be determined by the rotationalspeed of the tyre. Therefore, if the crane 10 operates at a speed abovea level that is suitable for a particular tyre, the tyre can be damagedand can rupture. Therefore, crane 10 may be configured to change betweenhaving one axle raised and having both axles engaged with the road, oncethe ground speed of the crane has reached a predetermined ground speedof the crane. The predetermined ground speed may be 1, 2, 3, 4, 5, 6, 7,8, 9 or 10+ km/h. Specifically, the predetermined ground speed may bearound 5 km/h.

In circumstances when the crane 10 is carrying a load and is operatingin crane mode, if the ground speed of the crane increases above thepredetermined speed, the crane 10 may lower rear wheel 16 and convertinto travel mode, even though the crane 10 is still carrying a load.Once the ground speed drops below the predetermined speed the rear tyreof wheel 16 can be lifted to convert the crane 10 back into crane mode.Converting crane 10 from two axle mode to three axle mode, even whenlifting and/or carrying a load, will sacrifice maneuverability, but canhelp to improve the damage, wear and lifespan of the tyres T1-T3 ofwheels 16, 18 and 20. In an embodiment, when in travel mode, crane 10can drive at highway speeds, for example 80 km/h or higher.

Conversion between travel mode and crane mode may be performed manuallyor automatically. Manual conversion may involve an operator instructingthe crane 10 to engage the tyres of wheel 16 with the road 21. Theoperator may be instructed by a signal from the LMI and/or PCL.Automatic conversion may help to reduce operator error. It may alsoallow a crane operator to simply drive from site to site without havingto worry whether or not the tyres of wheel 16 need to be engaged ordisengaged with road 21.

The first axle rear wheel i.e. wheel 16 may be raised and lowered usingair bag suspension systems, hydro-pneumatic suspension systems and/orsprings with auxiliary air bags or hydraulic cylinders to raise selectedaxles. The suspension system can employ integrated control by a LoadMoment Indicator (LMI) so that, at any time, control of the cranefunctionality and the suspension system may be coordinated. Conditionsthat may require changes to the suspension configuration can arise froma number of different crane components. Also, when in crane mode (e.g.FIG. 6), there are many conditions that can limit or over-ride changesto suspension configuration, or on other occasions actually trigger asuspension system change (e.g. going over the predetermined groundspeed). Therefore, the suspension system in crane 10 may be fitted withone or more sensors to monitor, for example, axle load, individual wheelload, axle height position, and wheel rotation speed. The LMI controlsystem may control the suspension e.g. hydro-pneumatic suspensionsystems and/or springs with auxiliary air bags or hydraulic cylinders,and the software in the LMI may take inputs from the one or more sensorsbefore making suspension system changes. The changes may be automatic,or they may alert a crane operator that the suspension system needsadjusting.

Other axle configurations that assist with crane operation can beincluded. For example, when traversing rough terrain to reach a jobsite, it may be useful to get higher ground clearance. If airbag orhydro-pneumatic suspension is utilised, then a high clearance mode maybe possible by adjusting the suspension. Each axle may be fitted withairbag or hydro-pneumatic suspension so that each axle is independentlycontrollable. Therefore, if a higher ground clearance is required, thesuspension system(s) of the axles that engaged with the ground may beraised. Each wheel may be independently controlled with its ownsuspension system. This may help to control individual wheel loads.Further, wheels on one side of the crane 10 may be raised relative tothe wheels on the other side. This may help crane 10 to adjust to unevenand sloping ground, and may help to stabilise the crane 10 whentravelling across an inclined surface when either in crane mode ortravel mode. For example, if crane 10 is travelling across an inclinethat slopes down to the right, the ride height of the wheels on theright may be increased to level the crane. This may be useful instabilising the crane when operating in crane mode since the load beingcarried will tend to exert a sideways tipping moment on the crane.

Having first and second rear axles, each for supporting the rear body onthe ground, via first rear tyre T3 of wheel 16 and second rear tyre T3of wheel 18, respectively, can also allow crane 10 to slew around onewheel. Slewing is the angular movement of a crane boom or crane jib in ahorizontal plane. With traditional two axle pick and carry cranes, aholding brake can be applied to one of the wheels and then three of thewheels are free to rotate in either direction. Therefore, duringslewing, the free wheels are able to rotate throughout the change inarticulation, with the pivot point of slewing being provided by thewheel to which the holding brake has been applied. When one of the cranebodies, e.g. the rear crane body 14, has two or more axles with tyres incontact with the ground, the slewing ability of the crane is diminishedor lost. For example, during any slewing movement, one or the two axleswould be dragged sideways during the operation. This can lead to verypoor tyre wear, and may also lead to vibration and a jerking movement ofthe crane during load carrying, which will affect crane usability andalso safety, as it can also induce load swing. Therefore, by having reartyres T2 of wheel 16 moveable between engaged and disengaged states, theslewing ability of crane 10 may be similar to conventional two axle pickand carry cranes when operating in crane mode.

Since crane 10 is able to lift and carry greater loads compared totraditional pick and carry cranes, the loads placed onto the front axleand front tyres 20 tend to increase. Referring to FIG. 7a , as theforward tipping moment increases, represented by TM₂, the loadtransferred to the front wheels 20 increases. The front tipping momentis calculated from the front tipping line, represented by dashed line40, which in the embodiment of FIG. 7a is determined by the front tyresT1 of opposite front wheels 20.

For embodiments where the boom 26 is telescopic, the forward tippingmoment TM₂ is dependent on the distance d₇ the load 32 is away fromwhere the tyres T1 of front wheels 20 engage the ground (forward tippingline), and the mass of the load 32. Therefore, the forward tippingmoment TM₂ increases as the boom length increases for a given load mass.The crane 10, therefore, must provide an adequate counteracting forwardtipping moment to prevent the crane 10 from tipping forwards. As anexample of a counteracting tipping moment, the centre of gravity of therear body 14 is positioned at dot 42. Therefore, the rear bodycounteracting tipping moment CM₄ is determined by the mass of the rearbody 14 and the distance d₄ of the centre of gravity 42 from the forwardtipping line 40.

The counterweight 22 also provides a counteracting forward tippingmoment CM₅ determined from its centre of gravity 37. More specifically,the counteracting forward tipping moment CM₅ is determined by the massof the counterweight 22 and the distance d₅ of its centre of gravity 37from the forward tipping line 40. Therefore, not only does counterweight22 help to maintain a counteracting side tipping CM₁ moment above athreshold value when the crane is lifting and/or carrying a load, it canalso help to maintain a counteracting forward tipping moment. However,the mass of counterweight 22 is generally less than the mass of the rearbody 14 and, since the centre of gravity 42 of the rear body 14 isfurther away from tipping line 40 than the centre of gravity 37 forcounterweight 22, CM₅ is generally much less than CM₄. In any case,provided CM₄+CM₅≥TM₂, the crane 10 should not tip forward on the tippingline 40.

Since TM₂ can increase or decrease depending on the mass of the weight32 and the length of boom 26, the crane 10 may be fitted with sensorssuch as load, distance, and angle sensors to determine TM₂. The one ormore on-board computers and/or computer system used to calculate TM₁ mayalso be used to calculate TM₂. TM₁ may be calculated at the same time asTM₂. TM₁ and TM₂ may be calculated in real time. One or more computersand/or computer systems can be used to calculate TM₂. If the one or morecomputers and/or computer systems determine that CM₄+CM₅≤TM₂, the crane10 may adjust the boom 26 so that CM₄+CM₅≥TM₂. Alternatively, the crane10 may warn an operator of the crane that TM₂ is approaching CM₄+CM₅.FIG. 7b shows the crane 10 is a position that is tipping forward. As thecrane begins to tip over the forward tipping line 40, the distance d₄and d₅ decreases to d₈ and d₉, respectively. Therefore, as the distanced₄ and d₅ decrease, the counteracting forward tipping moments CM₄ andCM₅ also decrease to CM₇ and CM₈, respectively. However, providedCM₄+CM₅≥TM₂ when the crane 10 first picks up the load when on levelground, as in FIG. 7a , the crane 10 should stay level with the tyres ofwheels 16 and/or 18 engaged as in FIGS. 2 and 6.

In crane mode, the loads being transferred through the front axle andtyre 20 are generally greater than those of the rear axles and tyres ofwheels 16 and 18 when carrying load 32. To accommodate this increase inload, the front axle may have a reactive suspension system. The frontaxle suspension system can be arranged to allow for a frame of the frontbody 12 to rest on and transfer load directly to the front axle during acrane mode. Therefore, the high forces can be transferred directly fromthe frame to the axle without stress to the suspension system (i.e.forces of up to about 56,000 kg). For example, if the suspension systemof the front axle uses airbags or other adjustable linkages, the bagsmay deflate and allow the frame of the front body 12 to drop and rest onthe front axle. Alternatively, to maintain the ride height of the crane,supporting members may extend from the frame of the front body 12 andengage with the front axle so as to take the load off the suspensionsystem and transfer weights and loads directly onto the front axle. Thismay be useful when the crane is operating on uneven ground and a highground clearance is required. Given the loads passed through the frontaxle and tyres of wheels 20 are greater than those passed through reartyres of wheels 16 and 18, the front tyres of wheels 20 may beconfigured to handle the increased loads. In the Figures, the front tyreof wheel 20 has a larger diameter when compared to rear tyres of wheels16 and 18. However, in some embodiments, the tyre diameters may be thesame, although the front tyre of wheel 20 would still be configured toaccommodate the increased loads when lifting and carrying a load.

While the embodiments disclosed herein incorporate both the firstcounterweight to improve the counteracting side tipping moment and therear suspension system that can be engaged and disengaged with theground, some embodiments may only have one of these features. Forexample, the crane may have only the first counterweight that can moverelative to the side tipping line on a crane that has two axles, such asa standard pick and carry crane. Alternatively, the crane may only havethe rear suspension system that can be engaged and disengaged with theground. However, the combination of using a first counterweight 22 thatcan move with respect to the tipping line and having a rear body 14 thathas two axles where one of the axles is arranged to be displacedrelative to the other such that tyres of the displaced axle canselectively engage or disengage with the ground, can provide a pick andcarry crane that can lift in the vicinity of 20% greater weights andprovide a counteracting side tipping moment increased by at least 25%compared with standard pick and carry cranes. This may be achievedwithout losing any ability for crane 10 to operate as a “taxi crane”,without losing slewing capability, with minimal impact on craneoperability and safety, and can preserve as closely as possible thecurrent maneuverability and turning circle while in crane mode. In anembodiment, crane 10 is configured to have a load moment rating of atleast 40 tonne.

In use, an operator would operate the crane so as to lift and/or carryload 32 using boom 26 from the front body 12. When the operator travelswith the load and has to turn, the moveable linkages pivot the frontbody 12 relative to the rear body 14 to form angle θ. By forming angleθ, side tipping line 34 is created. As shown in in FIG. 4, as thetipping line 34 is created, the counterweight 22 is moved from a centralposition of the crane and away from the side tipping line 34. In someembodiments, the counterweight 22 is not moved in unison with theformation of side tipping line 34. The counterweight 22 is moved so asto ensure counteracting side tipping moment CM₁ is greater than TM₁,which in some embodiments is combined with CM₂.

In FIG. 4, counterweight 22 is pivoted away from tipping line 34 aboutpivot point 30. However, if a moveable frame is used to move the firstcounterweight, the first counterweight is still moved away from sidetipping line 34 to maintain a counteracting side tipping moment. Thefirst rear axle of the rear body 14 is also engaged or disengageddepending on whether the crane 10 is operating in crane mode or travelmode. If the ground speed of crane 10 is above a predetermined groundspeed, such as 5 km/h, the first rear axle may be moved from adisengaged position to an engaged position to ensure excessive tyre weardoes not occur and/or loads are not exceeded. In this way, the operatorcan operate crane 10 to lift and carry loads.

FIG. 9 illustrates a further embodiment of a pick and carry crane 60.The pick and carry crane 60 is similar to the embodiments illustrated inFIGS. 1 to 8. The crane 60 has a front body 62 and a rear body 64connected by means of a pivot point 66. The rear body 64 has a forwardaxle 70 and a rear axle 68. Both the forward axle 70 and the rear axle68 support four tyres.

In this embodiment, the pick and carry crane 60 is provided withsteering to the wheels supported on the rearmost axle 68. The extent ofthe deflection provided to the wheels 72 a, 72 b, 72 c and 72 d attachedto the rearmost axle 68 by the steering is dependent upon the degree ofarticulation of the rear body 68 relative to the front body 62.

The steering to the rear axle 68 reduces the sheer forces experienced bythe tyres of the wheels attached to this axle. Furthermore, in thisembodiment, the steering applied to the wheels of axle 68 has a maximumdeflection. In the embodiment shown, the maximum deflection is 13°.However, it is to be realised that the amount of the maximum deflectionwill depend on the specific geometry of the crane to which this isapplied.

While the embodiments shown in the Figures describe an articulated pickand carrying crane having rubber tyres, the principles of the disclosuremay be extended to other forms of pick and carry cranes, for examplepick and carry cranes having crawler tracks.

In the claims which follow and in the preceding description of the pickand carry crane, except where the context requires otherwise due toexpress language or necessary implication, the word “comprise” orvariations such as “comprises” or “comprising” is used in an inclusivesense, i.e. to specify the presence of the stated features but not topreclude the presence or addition of further features in variousembodiments of the disclosure.

The invention claimed is:
 1. A pick and carry crane, the crane comprising: a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane; the front body comprising a front axle for supporting the front body on the ground; the rear body comprising first and second rear axles, each for supporting the rear body on the ground, each of the first and second rear axles supporting at least a pair of opposing wheels; wherein the first rear axle is arranged to be displaced relative to the second rear axle such that wheels of the first rear axle selectively engage or disengage with the ground; wherein the crane is adapted to operate in a travel mode in which the wheels of the first rear axle selectively engage the ground, and a crane mode in which the wheels of the first rear axle selectively disengage the ground; and wherein the crane is adapted to change from the crane mode to the travel mode at a predetermined ground speed of the crane.
 2. A pick and carry crane as claimed in claim 1, wherein the first rear axle is arranged closer to a rear of the rear body than the second rear axle.
 3. A pick and carry crane as claimed in claim 1, wherein each of the first and second rear axles comprises a respective suspension system, and wherein the suspension system for the first rear axle is arranged to displace the first rear axle to cause its wheels to selectively engage or disengage with the ground.
 4. A pick and carry crane as claimed in claim 1, further comprising a respective suspension system for the front axle, wherein the front axle suspension system is arranged to allow for a frame of the front body to rest on and transfer load directly to the front axle during a crane mode.
 5. A pick and carry crane as claimed in claim 1, wherein the crane is configured to have a maximum rated capacity of at least 35 tonnes.
 6. A pick and carry crane as claimed in claim 1, wherein the crane is configured to have a maximum rated capacity of at least 40 tonnes.
 7. A pick and carry crane as claimed in claim 1, wherein the front body is pivotally connected to the rear body to define the crane as an articulated pick and carry crane, and wherein wheels for the crane each comprise rubber tyres.
 8. A pick and carry crane, the crane comprising: a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane; the front body comprising a front axle for supporting the front body on the ground; the rear body comprising first and second rear axles, each for supporting the rear body on the ground, each of the first and second rear axles supporting at least a pair of opposing wheels; and steering for at least one set of rear wheels; wherein the first rear axle is arranged to be displaced relative to the second rear axle such that wheels of the first rear axle selectively engage or disengage with the ground.
 9. The pick and carry crane according to claim 8 wherein the steering is for a rearmost set of wheels.
 10. A method of operating a pick and carry crane having a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane, the rear body comprising first and second rear axles, each for supporting the rear body on the ground, each of the first and second rear axles supporting at least a pair of opposing wheels, the method comprising: displacing the first rear axle relative to the second rear axle to engage or disengage wheels of the first rear axle with the ground, wherein the wheels of the first rear axle are engaged with the ground when the crane is operated in a travel mode, and the wheels of the first rear axle are disengaged with the ground when the crane is operated in a crane mode; and changing from the crane mode to the travel mode at a predetermined ground speed of the crane.
 11. A pick and carry crane comprising a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane, the rear body comprising first and second rear axles, each for supporting the rear body on the ground, each of the first and second rear axles supporting at least a pair of opposing wheels, wherein the first rear axle of the pick and carry crane is operated using the method as claimed in claim
 10. 12. A method as claimed in claim 10, wherein an effective wheelbase of the crane is altered when the wheels of the first rear axle selectively engage or disengage with the ground.
 13. A pick and carry crane, the crane comprising: a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane; the front body comprising a front axle for supporting the front body on the ground; the rear body comprising first and second rear axles, each for supporting the rear body on the ground, each of the first and second rear axles supporting at least a pair of opposing wheels; wherein the first rear axle is arranged to be displaced relative to the second rear axle such that wheels of the first rear axle selectively engage or disengage with the ground; and wherein an effective wheelbase of the crane is altered by selectively engaging or disengaging the wheels of the first rear axle with the ground.
 14. A pick and carry crane, the crane comprising: a front body that defines a front part of the crane, the front body pivotally connected via a pivot arrangement to a rear body of the crane; the front body comprising a front axle for supporting the front body on the ground; the rear body comprising first and second rear axles, each for supporting the rear body on the ground; wherein the first rear axle is arranged to be displaced relative to the second rear axle such that wheels of the first rear axle selectively engage or disengage with the ground; wherein the crane is adapted to operate in a travel mode in which the wheels of the first rear axle selectively engage the ground, and a crane mode in which the wheels of the first rear axle selectively disengage the ground; and wherein the crane is adapted to change from the crane mode to the travel mode at a predetermined ground speed of the crane. 